Move domain - stupid me - need help

I have a domain with the server ONE.COM and my blog and page is created at MAC’s own integrated program; iWeb.

I want to keep my domain with One.com and create a new site her at wordpress, but I don‘t like the endings of the blogadress; example.wordpress.com.

So what I need is some guidance to remove my domain from One.com to WordPress, and how I can create a blog/site her at wordpress without having to find a NEW name for my site. When I try to create a new site I only get the message "domain-name" is taken obviously since I used it for my domain at One.com....